Overvoltage protector



July' 17, 1951 R. L.. BROWN 2,56%629 ovERvoLTAGE PROTECTOR original Filed oct. 15, 1947 ATTORNEY Patented July 17, 1951 OVERVOLTAGE PROTECTOR Robert Lurown, Teaneck, N. J., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Original application October 15, 1947, Serial No.

779,992. Divided and this application October 5, 1949, Serial No. 119,724

4 Claims.

This application is a division of Application Serial No. 779,992, led October l5, 1947, and relates to overvoltage protection for electrical generator systems and more particularly to improvements in the system and protector of the type shown in the copending application for U. S. Patent Serial No. 701,322, led October 4, 1946, now Patent No. 2,522,601, issued September 19, 1950, by Robert Lowell Brown.

An object of the invention is to provide overvoltage protection which does not respond to sudden surges of short duration of overvoltage.

It is desirable in the event of an overvoltage on one generator of a parallel arrangement that the other protectors do not trip due to surges caused by the nite time of operation of the faulted protector, reverse current relays, regulators and line switches. While the regulators of the normally functioning generators will automatically tend to keep the non-faulted protectors from tripping after a short, an object of the invention is to provide means for effecting an imrrediately acting time delay (of short duration) to keep the protectors from tripping before the regulators can take over.

Another object of the invention is to provide an immediately acting time delay (of short duration) for the protectors which is introduced by the use of short circuiting slugs (rings) of copper arranged` concentric with the coil on the electromagnet. Thus with the time delay in the protectors plus the correcting action of the regulators the non-faulted protectors will not trip when a parallel system is disturbed by an overvoltage generator.

The above and other objects and features of the invention will appear more fully hereinafter from a consideration of the following description taken in connection with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example.

In the drawings the single gure is a diagrammatic representation of a generator system embodying the invention.

The purpose of the overvoltage protector device, heretofore described and claimed in the parent application, Serial No. 779,992, led October l5, 1,947, is to prevent damage to an airplanes electrical equipment when malfunctioning of a generating system causes excessively high volt- The protector device is arranged to open the field circuit of the malfunctioning generator and in addition to effect the disconnection of its control equipment from the generator and to disconnect the generator from the main line Without arecting other generating systems connected,

in parallel to the line. Each of said generating systems are provided with a like protector device.

A typical system according to the invention in which the protector device 32 may be used, is illustrated in the single iigure of the drawing and may include a generator 89 having a eld Winding 8| and an interpole compensating winding 82. Output line 33 of the generator B is grounded, while output line 94 may be connected to a main bus line 85 through a line switch 99V operated bya solenoid 81.

The control equipment for the generator is in-y dicated generally by the numeral 90 and may be of a type described and claimed in the copending application Serial No. 621,515, filed October l0, 1945, by William R. Holmes.

The control equipment 9|] includes a variable resistance carbon pile 9| connected in series with the generator eld 8| through a conductor 92. The field 8| is connected through conductor 93y to output line 83 and the opposite end of the car-- bon pile 9| may be connected to the output line 84 through a conductor 94 and the main switch contacts 55 and 56 of the protector device 32.

The variable resistance carbon pile 9| may be controlled by an adjustable armature 95 shown schematically in the drawing and which may be of a type described and claimed in U. S. Patent No. 2,427,805, granted September 23, 1947, in the name of William G. Neild and assigned to Bendix Aviation Corporation. f The armature may be controlled by an elec-` tromagnetic winding 95 which may be connected across the generator output lines 83 and 84' by grounded conductor 97 and conductor 98. The conductor 98 may be connected to line 84 through switch members ll-45 of the protector device 32, Connected across the interpole compensatingv winding S2 by a conductor 99 and grounded conductor 99A is a potentiometer |00 having a center tap |00A connected to a compensating winding I0| for affecting the carbon pile 9| so as to maintain a predetermined division of load between the several parallel connected generators as is explained in the aforenoted copending application Serial No. 621,515.

The opposite end of the compensating winding |0| may be connected to an equalizer line |62 through a conductor |03, relay switch |94, andA switch members 44A and 45A of the protector device 32. The relay switch |04 is controlled by an electromagnetic winding |05 connected across the output lines 83--84 by grounded conductor lS including resistance IDEA, conductor 98 and'- switch contacts 44 and 45 of protector 32.

The relay Winding |95 is controlled by a pilot switch |01 biased by spring tension to the posin tion shown so as to close switch contact |00. Switch |01 is connected to conductor 98 while contact |08 is connected to conductor |06 so that upon switch |81 closing contact |08, relay winding |05 is shunted out of operation.

The pilot switch |01 is controlled by an electromagnetic winding |09 connected through conductor 98 and switch contacts 44--45 of the protector device to output line 84 and through grounded conductor H to output line 83.

Upon the output generator voltage rising above a predetermined value the relay switch arm |81 is biased by relay |09 so as to open Contact |08 and close a contact The latter action opens the shunt circuit of relay winding |85 causing the winding to close switch |04 whereupon the compensating winding I0| is connected into operation and to the equalizer line |82.

Moreover upon relay switch |01 closing contact a current winding |2 is connected across the open line switch 96 by a conductive passage leading from line 84 through switch contacts 44-45 of the protective device 32, conductor 98, switch |01, contact current winding l2, and a conductor I3 to the main bus line 85. The winding |2 is wound about a permanent magnet I4 and is arranged to cooperate therewith so that upon a current flow from the generator 88 to the main bus line 85 the magnetic eiiect of coil |i2 and permanent magnet H4 will exert an additive ilgct biasing a relay switch ||5 to close contact The relay switch ||5 is connected by a conductor ||1 to conductor 94 and through switch contacts 55 and 56 to the output line 86. The contact ||6 is connected by conductor ||8 through the switch contacts 46-41 of the protector device 32 to the line relay 81. The closing of switch l5 will then cause energzation of the line relay 81 and the closing of the line switch 86 which will shunt differential current winding ||2 out of operation.

Y Cooperating with the winding ||2 is a second current winding connected across the interpole compensating winding 82 through conductor |2| and grounded conductor |22. So long as the current flow is from the generator 88 to the main line 85 the winding |28 will exert an additive effect with the permanent magnet i4 tending to hold the control switch |5 closed. Howe ever, in the event the output of the generator 88 decreases to such a point that the current output of the generator is below that of the main bus line 85, then the winding |20 will exert a diierential effect with the permanent magnet lili tending to decrease the magnetic effect acting on the relay switch ||5 so that the switch I|5 under spring force is biased to a position opening conn tact I6. The latter action deenergizes the winding 81 causing line switch 86 to open.

As shown schematically in the drawing, switch contacts 46-41, I4-55, 55-56, MEA-435A, and dBA-41A may be closed by manually actuating the push rod 24. The same may be latched in the latter position through action of the latch mechanism 2| as heretofore explained.

The closing of switch contacts ABA-61A connects a sensing coil, the electromagnetic winding l07 across the field 8| of the generator 88 through conductors |30 and |3|.

When the voltage across the field 8| reaches a predetermined excessive value for any reason, the sensing coil l0 actuates the armature i5 and through the studs 35 the latch 2|, thus releasing the reset rod 24 and opening the main contacts 55-58, and the four pairs of auxiliary contacts 46-41, 44-45, 14A-45A, and NA-41A.

In the latter event the following action takes effect. The contacts 48-41 open the potential circuit for the line relay 81 and thereby cause line switch 86 to open and eiect deenergization of current winding |20. The contacts 44-45 open the potential circuits for the carbon pile voltage coil 96, relay voltage coil |85, and relay voltage coil |00. Deenergization of coil |00 causes in turn relay switch |01 to open contact and thereby the circuit to differential current coil ||2. The main contacts 55--56 open the generator eld circuit. The auxiliary contacts 44A and 45A open the circuit of the compensating winding |0|. The auxiliary contacts 46A and 41A open the circuit of the sensing coil |0.

As an alternative arrangement the switch MA-45A may be lnormally open so that upon the latch 2| releasing the reset rod 24 the switch 44A-45A may close a circuit to energize a warning device such as an electric light or bell to indicate that the overvoltage protector has disconnected one generating system from the main bus.

As shown diagrammatically in the drawing, a plurality oi generators 88, 88A, 88B and 82C may be parallel connected to the main bus line 85. Each of the generators 88A, 80B and 88C has similar control equipment to that indicated gern erally by numeral 68 and indicated herein as 98A, 08B and 99C, respectively. Likewise the generators 86A, 38B and 88C have protector devices similar to the protector device 32 of the generator 80 and indicated herein as 32A, 32B and 32C, respectively.

Surge voltages due for example to a faulted generator will not actuate the overvoltage protector of the other non-faulted generators. This condition is achieved by the incorporation of the copper washers 1|, which act as shorted turns on the sensing coil l0. Such, shorted turns in an inductive system, generate flux that opposes the flux generated by the coil |8. Thus during change in the energizing current of the coil this opposition retards the build-up of Suiiicent coil flux to actuate the armature i5, so as to provide a sufficient time lag to prevent tripping of the latch 2| by surge voltages. This time lag is further insured by the construction of the armature i5 and latch 2|. The armature l5 has studs 35 arranged to trip the latch '2| ai" ter the armature has traveled about two-thirds of its distance to the eicctromagnet I0. This construction also permits the tripping voltage to be unaffected by friction.

Once the overvoltage protector has operated the reset rod 24 may be pushed down to reset the mechanism by manually compressing the bellows 34.

Although only one embodiment of the invention has been illustrated and described, various changes in the forni and relative arrangements or" the parts may be made to suit requirements'.

What is claimed is:

l. In combination, an output line, a plurality of generators connected to said output line, each of said generators having a eld circuit, control means responsive to the current now through the iield of each generator for disconnecting the as sociated generator from the output line upon a rise in field current above a predetermined value, and time delay means for retarding operation of ,said control means upon a voltage surge in excess of a predetermined value affecting the control means.

2. The combination defined by claim 1 in which said control means includes an electromagnetic Winding and relay switch means operated thereby and associated with each of said generators; and said time delay means includes a short circuted turn about said Winding and so arranged. as to retard disconnection of the associated generator upon a transitory voltage surge affecting said Winding.

3. In combination, a main output line, a plurality of generators, each of said generators having a field circuit, an output voltage regulator and a reverse current relay means to control the connection of the associated generator to the main output line; the improvement comprising an overvoltage protective relay means associated with each generator and arranged to effect the REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Name Date Almassy Sept. 27, 1949 Number 

